The present invention relates to a support structure for supporting a lift crane and in particular to lifting cranes for use on jack-up type drilling rigs, lift boats, platforms, boats and the like, wherein the lift crane is positioned about a leg(s) of the jack-up structure atop the jack-house or yoke assembly.
The preferred embodiment of the present invention contemplates a system for elevating a lift crane above the deck and about the leg of the jack-up structure, without relying upon the leg for structural support, unlike king post-type design lift cranes. A structurally reinforced jack-house or yoke assembly having jacking units interfacing with the leg, is provided at the deck of the vessel. The jack-house or yoke assembly is configured to engage and support a crane tub upon the top of the jack-house or yoke assembly, which crane tub has situated thereupon the lift crane.
The structurally designed jack-house or yoke assembly allows one to support a crane above the deck in a stable manner independent of the leg situated there through, so as to provide a superior structural support for the lift crane, while providing ample space within the jack-house or yoke assembly for the jacking units. The combined jack-house/yoke assembly support structure thereby affords significant space savings upon the deck of the platform, while providing enhanced support of the lift crane.
Both jack-up drilling rigs and lift boats are well known in the art. These vessels are moved from one location to another via a floating hull. Lift boats are self-propelled while jack-up drilling rigs are towed to a location. Lift boats have cylindrical pipe legs while jack-up drilling rigs tend to have truss legs. However, some older generation jack-up drilling rigs have pipe legs. Once the vessel has reached the desired location, the legs are lowered to the seabed.
The hull continues to be lifted until it is above the water""s surface. When the vessel reaches the desired height above the water""s surface, the vessel provides a stable work area to perform various operations. As in the case with a jack-up drilling rig, the vessel is used to explore for oil and/or gas. In the case of the lift boat, a number of work related activities could be accomplished once the vessel has reached its operational position. Generally, lift boats have not been used in actual drilling operations. Both vessels employ the use of various crane arrangements to facilitate operations.
A list of patents which may have some pertinence to the present invention include:
In the past, cranes have been mounted in essentially three configurations on jack-up vessels. First, the most common method is to mount the crane in a strategic location on the deck. The drawbacks of this mounting method have been both using up valuable deck space and the legs getting in the way of the movement of the hook load.
A second method that has been employed on cylindrical pipe leg lift boats has been to mount the crane around the pipe leg/cylindrical guide tower utilizing a pair of resilient pads spaced apart to enable rotation of a cylinder around the leg (See U.S. Pat. No. 4,652,177, Gunther, Jr. et al, Mar. 24, 1987).
Another patent was issued that provided a method and apparatus for mounting lift cranes on cylindrical pipe leg vessels using a pair of bearing races spaced apart to allow for unencumbered vertical movement of the leg (See U.S. Pat. No. 4,417,664, Gordon, Nov. 29, 1983). The third method of mounting the crane is to mount the crane around the leg with the ring beam base mounted directly on the deck of the vessel about the leg (U.S. Pat. No. 5,580,189, Sanders et al, Dec. 3, 1996).
Jack-up vessels utilizing truss type legs require a jack-house or yoke assembly to provide the necessary structural integrity for the upper guide assembly. A jack-house is generally a square or rectangular structure designed to provide the necessary structural integrity to support the upper guide assembly. The guides on a jack-up vessel are used to guide the legs through the hull as the legs are being elevated or lowered. A yoke assembly is another method to tie the upper guides structurally to the hull. The lower guide assembly is generally incorporated into the lower part of the hull. The motors and gears (gear case) used to lift and lower the legs in some cases are attached to this jack-house or yoke assembly. However, the upper guides and the gear cases may be separate and independent of each other.
Deck space is at a premium on jack-up vessels and deck mounted cranes take up valuable space. Lift cranes employing a tubular tower arrangement are limited to the maximum diameter of cylindrical pipe leg vessel designs thus limiting the working water depth of the vessel.
In summary would appear that the prior art has failed to contemplate a lift crane and support structure therefore which provides the lift capability and stability of a deck mounted crane, but mounted in an elevated fashion about a leg upon a jack-up structure, while providing space savings and a cost effective design.
The present invention contemplates a lift crane and support-structure-system which provides space efficiency in the form of an elevated support above the deck but with more enhanced capabilities than tubular tower arrangements and deck mounted cranes.
The vessel of the present invention utilizes a conventional jacking mechanism to elevate and lower the legs while the jacking units are independently supported upon the deck in the vicinity of each leg. In the preferred embodiment of the present invention, a structurally reinforced jack-house or yoke assembly having jacking units interfacing with the leg is provided at the deck of the vessel. Unlike traditional jack-houses or yoke assemblies which are used to only provide the necessary structure for the upper guide assembly and/or the gear cases, the jack-house or yoke assembly of the present invention is substantially reinforced structurally to support a crane tub thereupon, which the crane tub in turn has situated the lift crane.
The jack-house, although from the exterior may appear to be similar to prior art jack-houses, employs significant structural reinforcement to withstand the heavy tonnage loads which may be exerted upon it by the lift crane in operation. The jack-house utilizes extensive vertical structural support within its walls, which can be in the form of box/tubular beams, T-beams, or I-beams, which run through the deck to the hull, interfacing with the frame of the vessel (longitudinal and transverse bulkheads) and providing a support perimeter along the top edges of the jack-house above the wall sections including the vertical structural supports.
Using the yoke assembly method of support, the diagonal bracing and support structure is likewise significantly structurally reinforced to withstand the crane loads. With the yoke assembly, additional diagonal bracing and support structure will be required based on crane structural requirements.
The circular crane tub is primarily supported upon the structurally enhanced jack-house. Further, within the hull, angled or bracing support members interfacing within the vessels longitudinal and transverse bulkheads are employed to support the vertical structural support members in a generally vertical support position. Box/tubular beams, T-beams, I-beams, or the like, whose ends engage the vertical structural supports, are situated below the horizontal upper surface or roof of the jack-house to add further structural stability to the roof. Using the yoke assembly method of mounting, the circular crane tub is similarly situated.
In the preferred embodiment of the present invention, a crane tub having an exterior diameter which is about the same as the width of the jack-house is situated upon the top of the jack-house so that the diameter of the crane tub engages the horizontal upper surface or roof of the jack-house above the vertical structural supports, so that the vertical structural support members support the crane tub. Portions of the crane tub, which do not engage the vertical structural supports, may engage the horizontal support employed below the roof of the jack-house.
The combined jack-house/crane tub design allows one to support a crane above the deck in a stable manner independent of the leg situated there through, so as to provide a superior structural support for the lift crane, while providing ample space within the jack-house for the jacking units. The combined jack-house/crane tub support structure thereby affords significant space savings upon the deck of the platform, while providing enhanced support of the lift crane.
The outer walls of the jack house are formed from heavy-duty planar support panels which are extensions of, or otherwise conjoined to corresponding longitudinal and transverse bulkheads within the substructure of the vessel, so as to provide a heavy duty load cell emanating through the deck of the vessel, so as to form a combined jack house structure/lifting apparatus support platform.
In an alternative embodiment of the present invention, an array of truss support beams are provided in communication with underlying longitudinal and transverse bulkheads in the vessel substructure (so as to form a xe2x80x9cload cell), to provide a raised platform for the lifting apparatus, while providing an unencumbered, open area upon the deck under said platform for inspection of underlying gear cases and related components.
It is therefore an objective of the present invention to provide a lift crane support structure which utilizes a minimal amount of deck space.
It is another objective of the present invention to provide a lift crane support structure which supports the lift crane above the surface of the deck and about a jack-up leg, but does not rely upon the jack-up leg for structural support.
Another objective of the present invention is to provide a lift crane support structure which supports a lift crane above the surface of the deck but with greater structural stability and capacity than other prior art designs.
Lastly, it is an objective of the present invention to provide a method and system for supporting a lift crane over the deck of a vessel and about a jack-up leg, which the system further employs a structurally enhanced jack-house as a component of the support system and also is utilized to shelter the jacking units in an unencumbered fashion.